The ABS warning light came on this afternoon but the first red light I came to I switched the ignition off and back on and it went out and stayed out. Now, when I test drove the car back in December, the light came on, but when the dealer tried it there was no fault to see and obviously it has been fine since then. Is this likely to be a dodgy sensor? I have VCDS Lite. Will that be of any use in determining the problem?

Scan of ABS module should tell you a fault code that goes with the warning light.